While I can understand why someone from present times would not want to describe the fact that all oil drains back to the pan on shut down of the engine as a "design feature", nevertheless, it was, I believe, part of the design of the engine. a lot of harleys for example, currently have this element as part of the design. if an engine is designed by someone or a team of someone's, then all parts of the engine and how it works is designed by them. at the very least, such things are taken onto account during design so that the engine as a whole still functions. considering the age of the design, its intended use, how its maintained and by whom and how often. not to mention all the engines that came before it and building upon that library of knowledge and experience I believe makes it a design feature of the engine. I don't think one could describe the drainback as just something that kinda happened during its construction or was overlooked or not considered or possibly not integral to the proper function of the engine from the perspective of the designer(s). no disrespect to anyone or their viewpoint, just another perspective to throw into the discussion.